Signaling system



July 28, 1925. 1,547,771

R. c. MATHES S IGNALETG SYSTEM Filed' March 24, 1921 Patented J ulyql28, 1925.

UNITED ASTATES ROBERT c. Marlins, or NEW YoRx, N. Y., lAssIaNoR To WESTERN ELEorRIcvcom 1,541,171 PATENT OFFICE.

PANY. INCORPORATED, OF NEW YORK, N. AY., A CORPORATION OF NEW YORK.

SIGNALxNG SYSTEM.

Application led March 24,1921.. Serial No. 455,136.

To all whom it may concern:

Be it known that I, ROBERT C. MATHES, a citizen of United States, residing at New York city, in the county of Bronx,

State of New York. have invented certain' new and useful Improvements in-Signaling Systems, of which the following. is a full. clear, concise, and exact description.

This invention relates to signaling systems and more particularly to systems employed in connection with'long distance telephone lines.

Vith long distance telephone lines, where it is the practice to use conductors composited forboth telephone and telegraph operation, it has been found necessary, to avoid disturbing the telegraph instruments, to use signaling current of a frequency considerably higher than 16 cycles per second, which is the approximate frequency of the current generally used to operate the ordinar'y type of low frequency telephone ringer. To signal over composited lines with the higher frequency current, it has been the practice to useareceiving circuit in which is eonnecteda .relay having an,

armature tuned to respond to current of approximately 135 cycles per second.

To maintain satisfactorily this system, it is necessary that the tuned relay and its associated relays be maintained in careful adjustment to prevent interference from low frequency current or stray line currents due to the telegraph operation or some eX- ternal source. With the advent of telephone lines upon which repeaters are installed, and which are designed for most effective operation on currents of voice frequency range, it is found necessary to provide a special circuit at repeater stations to have efficient means for ringing through the repeater station with the current of 135 cycles.

It is the object of this invention to provide an improved signaling system similar to but more easily maintained, than the system described above, and which is more free from interference, and is better adapted for operation on lines to which repeaters or other apparatus designed for voice frequency currents are connected.

Broadly, it is the ob]ect of this invention to provide a signaling s stem in which a receiving device respon s to a predetermined, seleced and combined effect of several electrical impulses applied to the transmission medium simultaneously, with means for preventing the response of the receiving device to impulses having frequenc components differing from those on which the receiving device is designed to respond.

rIto attain this object, current impulses of various selected frequencies are applied to the transmission medium simultaneously,

and the receiving apparatus is designed `to respond to some predetermined joint edect resulting from the combination of the various component impulses.V For example, in the case of two currents of different frequency, the receiving circuit may be designed to respond to the difference frequency. `Similarly, other resultant effects of the combining of the several components may be selected and. used to operate the receiving apparatus. To avoid false signaling, the receiving circuit is designed so that it responds to the impulse of predetermined frequency only when thatis obtainedas a result of the combining of the particular component frequencies of the same value as those. selected for operation. 1n view of the fact that it is unlikely that the several components of the interfering impulses are identical with the several components of the operating impulses, the possibility of false operation is remote.

The nature of the'invention will clearly appear from the following specification and the accompanying drawing, Figure 1 ot which shows diagrammatically one embodiment thereof as applied to a telephone transmission line where in` two speech frequency currents arel simultaneously applied tothe line. Fig. 2 shows a receiving circuit adapted to be employed in connection with the transmission line L when three speech frequency currents are substituted for the two current'sources shown at 18, Fig. 1.

Figure 1 of the drawing shows how this signaling system may be applied to a. telephone transmission line L connecting two stations A and B. To signal the station B, the plug 34 of a cord circuit C, located at bothstations A and B, but shown only at station A, is inserted Ainto a jack 1 and a ringing key 2 is actuated causing the operation of a relay 3 which applies from a source 18 two frequency current to the line L. This current passes by induction through the windings of repeating coils 40 and 41 and over the line, to a receiving circuit X (which is shown within the dotted lines of the rectangle), through a selective circuit to a coil, 10 and then through the circuits of thermionic tubes 11 and 12.

'The output side of tube 12 supplies unidirectional current to a relay 13 which operates and causes the release of a normally operated relay 14, the operation of relay 35 and the lighting of the lamp 47, indieatin that station A is calling. By select. ing the two fre uency components so that their difference requency is below that of\ the voice range, the selective circuit is, in

. general, not required since the input circuit of tube 12 then has low transmission etticiency for currents of voice range fre- `quency.

The repeating coils 40 and 41 areshown connected in the line circuit to form with re- -lays 42 and 43, and keys 44 and 45, one leg of a composite telegraph circuit. This cir cuit is'shown merely to illustrate a source of interfering currents, which the circuits of this invention prevent from causing a false operation of the line signals at stations A and B. It is thought that the invention may be more fully com rehended from the following detailed description of the operation of the system.

Assuming that it is desired to signalthe station B from the station A, plug 34 of cord circuit C is inserted into jack 1. Relay 15 then operates through the following circuit:

from grounded battery, through the winding of relay 16, sleeve contacts of plug 34 and jack 1, and windings of relays 15 and 17 to ground. Relay 15 by its operation connects, through its alternate Contact, conductor 31, from the receiving circuit Y, to its lower winding terminal, the reasons for which will hereinafter appear. The marginal relays 16 and 17 do not operate at this time. However, on the actuation of ringing key 2, the winding of relay 16 is shortcircuited, by the connection of battery to the lower rightehand contact of the key 2, and relay 17 operates. Relay 3 operates through an obvious circ-uit and applies to the conductors of transmission line L doubletrequency ringing current from the source 18.

For purposes of description, it may be as- .denser 7. These circuits are resonant to .grid circuit of tube 11.

their respective 'frequencies and offer high impedance to other frequencies. A resultant current, due to the joint eect of the two components passingv through coil 8, is induced in the secondary coil 10 of trans' formerl 9. This induced current passes through the condenser 19 and shunting resistance 20 into the-grid circuit of the tube The effect of the condenser and resistance is to assist rectification in the grid circuit and to produce the current component of beat or difference frequency. In the plate circuit of the/tube 11 is battery 21 in series with a condenser 22 shuntcd by an inductance 23. This plate circuit is designed to offer high impedance to the difference frequency and offer low impedance to other frequencies. Consequently, current of the beat or difference frequency is induced in the secondarycoil 24 of the transformer '25.' This induced current passes through the grid circuit of the tube 12 which includes a condenser 46 shunted by a resistance 26.' This condenser and resistance in the grid circuit have the same' rectifying effect as 'lid condenser 19 and resistance 2'? of the The effect of this is to produce-a direct current potential .in the grid of this tube. In the plate circuit of tube 12 is connected the winding of the relay 13 which is energized by the corre'- sponding ainpliicd unidirectional current. Although thermionic rectifying tubes are shown, it is to be understood that any other suitable rectifying devicemav be used -to produce the beat frequency. The actuation of relay 13opens an obvious circuit through the winding-of the normally operated relay 14, which, in releasing, closes a circuit through the left-hand winding of relay 35, and leftfhand normal contact of relay 27. Relay 35 operates and illuminates, through an obvious circuit, lamp 47 thereby signaling station B that station A is calling. Relay 35 in operating locks up through a circuit including grounded battery, its right- .hand winding and left-hand contact andthe right-hand normal contact of relay 27 to ground. The operator at station B, in re spense to the illumination of lamp 16 inserts 'into a jack 28 the plug 34 of cord circuit C located at station B. This causes the operation of-relay 27 through a circuit similar to that traced for the operation of relay y15. Relay 27 in operatineopens at its right-hand normal contact, the locking circuit of relays 35 which releases and extinguishes lamp 16. Marginal relay 36 and 16 are not operated at this time. A conversational path is now completed between stations A and B over the line L, and subscribers lines associated with the respective stations may be connected by any ofthe well known methods used inV connection with local switchboards.

If, during the conversation it is desired to liu) Asignal the operator at station A, relay 29 is operated by the actuation of the ringing key 2 in the same way that relay 3 is operated. Relay 29 in operating applies double frequency ringing current to the line L from the source 38. This current passes over the line through the normal Acontacts of relay 3v into the receiving circuit Y which is similar to the receiving circuit sho-wn associated with ,station X. A'normally operated relay similar to relay 14 -is caused to release and places ground on conductor 31 which short-circuits the winding of -relay 17 through the right-hand alternate contact of relay l5, which is in the operated condition by reason of the previous insertion of plug 34 into jack 1. This causes a reduction in the resistance of the circuit of marginal relay 16 which now operates and causes the illumination of the lamp 32 through an obvious circuit, notifying the operator at station A that station desires to converse. The listening key 37 is then actuated, connecting an operators telephone set, (not shown), to the conductors of the cord circuit, thereby establishing a conversational connectionwith the 'operator at station B. When relay 16 operates it locks up through a circuit including grounded battery, its winding and the left-hand contact,

.l resistance 39 and the lower left-hand normal contact of key 37 to ground. This locking circuit is opened when key 37 is actuated. Relay 16 accordingly releases and 1 extinguishes lamp 32.

Since the apparatus at either end of the line L is similar, a signal may be similarly transmitted from station B to station A to operate rela)7 30 and cause the lighting of lamp 33 in the same manner as relay 35 is operated and lamp 47 illuminated as previously described.

lVhen the cord circuit plugs at each sta.- tion are withdrawn from their respective jacks, it is evident that the circuit paths through the sleeve relays at each station are opened so that these relays then release and all apparatus is restored to normal.

'lhe preceding description explains how a two frequency source of current may be applied to a long distance telephone transmission line. It is evident, however, to one skilled in the art, that a source. of ringing current consisting of more than tWo frequency-components might be used if desired witha slight modification of receiving circuit X. In that event,l assuming for instance, instead of a two component source of current as shown at 18, a three component source is used. It would then be necessary to use a selective circuit composedI ofy 1. The method of operating a signal over a transmission line designed to efficientlyl transmit voice frequency currents which comprises simultaneously applying a plurality of audio-frequency currents to vsaid line, separately lreceiving the different components of said simultaneously applied currents, combining' the different components, integrating the beat frequency component 'of said combined audio-frequency currents, rectifying the bea-t frequenc-ycomponent, and translating the rectified current into a signal.

2. In a signaling system, a telephone'line designed for the efficient transmission of speech frequency currents, means for transmitting a pair of fixed frequencies over said line simultaneously, means associated with said line for combining said frequenciesto produce a difference frequency, said difference frequency being within the voice range, a signal, and mea-ns associated with said line responsive to the difference frequency for operating said signal.

3. A transmission line divided into an inner and two outer sections, devices for inductively uniting the three sections, means associated with the inner section ,for app-lying electrical current to said inner section for transmitting telegraph messages thereover, means associated with one of the outer sections of said line for applying at will a pair of audio-'frequency currents to said line, means associated with the other outer section of said line for combining said frequencies to produce a beat frequency, and a signal controlled by said beat frequency.

4. In combination, a transmission line, means for transmitting telegraph messages thereover, means for applying simultaneously a pair of speech frequency currents at will to said line whose difference frequency is within the voice range, and a receiving circuit including a tuned circuit for each of said -speech frequency currents, means for combining the pair of speech frequency currents to produce the difference frequency, a circuit resonant to the difference frequency, and a signal device actuated by the difference frequency.

5. In a signaling system, a transmission lili) line composited for simultaneous telephony rents and for transmitting a definite com bination of audio-frequency currents over said line, means at the other end of said line responsive only to said definite combination of audio-frequency currents lto produce a unidirectional current, a signal and means to actuate said signal responsive to said unidirectional current.

6. In a signaling system, a transmission line composited for simultaneous telephony and telegraphy, means at one end of said line for transmitting aiulio-frequency currents and4 for transmitting a definite coinbination of audio-frequency currents over said line, a. plurality of circuits at the other end of said line respectively resonant to the component frequencies of the definite conibination of audio-frequency currents transmitted over ,said line, signal controlling means responsive to a predetermined combination of the incoming audio-frequency currents, and a tuned circuit inductively coupled with said resonant circuits selectively sensitive to the predetermined combination of incoming frequencies for effecting the operation of said signal producing means..

7. In a signaling system, a transmission line composited for simultaneous telephony and telegraphy, a link circuit for extending said line, means associated with said link circuit for transmitting audio-frequency currents over said line, a plurality of current sources of different frequencies within the range of audibi-lity, manual switching means associated with said link circuit for applying said current sources to one end of said linel simultaneously, receiving means at the other end of said line consisting of a plurality of circuits, each resonant to a different one of said simultaneously applied audio-frequency currents, a plurality of thermionic tube circuits for integrating the difference frequency component of the simultaneously applied audio-frequency currents and for rectifying it, and signaling means responsive to sai-d rectified current.

8. In a signaling system, a transmission line composited for simultaneous and telegraphy, a link circuit for said line, means associated with said'link circuit for transmitting audio-frequency -currents over said line,- a plurality oftcurrent sources of different frequencies within the," range of audibility, manual switching means associated with said link circuit for applying said current sources to one end of said line simultaneously, receiving means at the other rend of said line consisting of a plurality of circuits, cach reso-nant to a different one of said simultaneously applied audio-frequency currents, two thermionic tubes inductively coupled with said resonant circuits, the output circuit of one tube tuned to the difference frequency of the simultaneously applied audio-frequency currents and the other of said tubes reetifying the difference frequency current, and signaling means resp01isive to the rectified current.

9. In a signaling system, a transmission line designed to efiiciently transmit voice frequency currents, a link circuit for said line, means associated with said link circuit for transmitting audio-frequency currents over said line, a plurality of current sources of different frequencies within the range of audibility, manual switching means associated with said link circuit for applying said curi-ent sources tol one end of said line simultaneously, responsive means at the other end of said line consisting of a plurality of circuits, each resonant to a different one of said simultaneously applied audio-frequency currents, two therinionic tubes inductively coupled with said resonant circuits, the output circuit of one tube being tuned to the difference frequency of the simultaneously applied audio-frequency currents and the other of said tubes rectifying the difference cui'- rent, and signal ine-ans responsive to the rectified current.

In witness whereof, I hereunto subscribe my naine this 2l day of March, A. D. 1921.

ROBERT C. MATHES telephony 

